Flame detector utilizing an ultraviolet sensitive geiger tube



Sept. 19, 1967 FLAME DETECTOR R. AXMARK 3,342,995

UTILIZING AN ULTRAVIOLET SENSITIVE GEIGER TUBE Filed July 20, 1965 w FUSE TYPE b Z IMPEDANCE+ H OUTPUT lo I2 5 I -|9 CATHODE m A.C. LINE ANODE LII INVENTOR. ROGER E. AXMARK ATTORNEY United States Patent 3,342,995 FLAME DETECTOR UTILIZING AN ULTRA- VIOLET SENSITIVE GEIGER TUBE Roger E. Axmark, Fridley, Minn., assiguor to Honeywell Inc., Minneapolis, Minn., a corporation of Delaware Filed July 20, 1965, Ser. No. 473,450 6 Claims. (Cl. 250-83.6)

My invention is concerned with an improved condition detecting apparatus and particularly with such an apparatus utilizing a Geiger tube as a condition sensing element, the apparatus having a simple and inexpensive combination power supply, quenching circuit, and output circuit construction to supply operating voltage to the Geiger tube, to quench the Geiger tube after a period of ionization thereof, and to provide an output indicative of the presence of a condition to which the Geiger tube is sensitive.

By Geiger tube I mean a condition sensor having an anode and a cathode disposed in an ionizable gas, and which, upon being subjected to a condition to which it is sensitive, causes an electron to be present within the electric field established by the anode and cathode, whereupon the electron accelerates toward the anode, ionizing the gas, and causing an arc discharge current to flow, which current must be subsequently quenched by means of an external circuit mechanism.

My invention is of particular utility when utilized as a flame detector portion of a combustion safeguard apparatus.

More particularly, by virtue of the simple and inexpensive construction achieved by my invention, my invention has utility as a flame detector utilized with small applicances having, for example, gas burners as a portion of the appliance. Generally, flame detectors may be characterized as thermocouple actuated, bimetal actuated, or photocell actuated. The photocell actuated flame detectors have a distinct advantage in that they are capable of detecting the presence or absence of flame in a very short time period, no more than a few seconds. However, prior art flame detectors of this type, which can be characterized as electronic flame detectors, have been unduly complicated and expensive, limiting their use to large burner installation.

My invention may utilize a Geiger tube which is responsive to ultraviolet radiation in the flame, and because of the unique construction of my invention, the operational environment required by a Geiger tube is provided with a minimum number of components.

More specifically, the construction of my invention is adapted to be connected directly to a source of AC voltage, such as the 120 volt, 60 cycle AC supply normally to be found in residences. I provide a transformerless voltage doubling network including a capacitor and a diode which is directly connected to the source of AC voltage to charge the capacitor on a first half cycle of the AC voltage. I further provide a Geiger tube having an anode and cathode disposed in an ionizable gaseous medium, with the anode and the cathode of the Geiger tube connected in parallel with the diode, the diode and the Geiger tube being poled so as to conduct on opposite half cycles of the AC voltage. In this manner, during one half cycle of the AC voltage the capacitor is charged, and on the other half cycle, the now charged capacitor is connected in aiding relationship to the voltage of the AC line as a source of operating voltage for the Geiger tube. In this manner, I am able to achieve operating voltages for the Geiger tube in excess of 200 volts.

When the Geiger tube experiences an ionizing event, as by the presence of flame, the Geiger tube is rendered conductive to energize output means. This period of conduction is limited to a particular half cycle of the AC line,

and on the succeeding half cycle the Geiger tube is substantially shorted by the above mentioned diode to thereby quench the Geiger tube during this half cycle of the AC line.

As a further feature of my invention, a fuse type current limiting impedance is connected in circuit with the capacitor. As yet a further feature of my invention, the output means consists of a relay connected in series with the anode and cathode of the Geiger tube and having a winding with a capacitor connected in parallel, the capacitor serving to maintain the relay winding energized during the quenching half cycle of the Geiger tube.

My invention will be apparent to those skilled in the art upon reference to the following specification, claims, and drawing, of which:

The single figure is a schematic representation of my invention.

Referring to the single figure, reference numerals 10 and 11 designate power input terminals adapted to be connected to a source of AC voltage. A first circuit means is connected between the terminals 10 and 11 and comprises a fuse type current limiting impedance 12, a capacitor 13, and a diode 14. Diode 14 is poled so as to conduct current to charge capacitor 13 when terminal 10 is positive with respect to terminal 11.

A second circuit means is provided consisting of output means 15 connected in series circuit with the anode and cathode of a Geiger tube 16, this series circuit being connected in parallel with diode 14.

More specifically, output means 15 consists of a relay having winding 17 and output switch means 18 adapted to be closed upon energization of winding 17. For purposes of simplicity, I have shown but a single switch 18 connected to conductors labeled output. It is within the teachings of my invention to provide a plurality of switches to be used for any particular output function.

Reference numeral 19 identifies a second capacitor which is connected in parallel with winding 17 and functions, as will be described, to maintain energization of winding 17 during the quenching half cycle of Geiger tube 16.

Geiger tube 16 includes a cathode electrode and an .anode electrode which are disposed in an ionizable gaseous medium contained within an envelope. Geiger tube 16 is constructed and arranged to be sensitive to a given radiation, for example ultraviolet radiation from a flame. The presence of this radiation causes the gas medium within the Geiger tube to ionize such that the Geiger tube becomes current conductive from the anode to the cathode. As can be seen in the single figure, the anode of Geiger tube 16 is connected to the cathode of diode 14. Thus, Geiger tube 16 and diode 14 are poled so as to conduct current during opposite half cycles of the source of AC voltage to which terminals 10 and 11 are connected.

Considering the operation of my invention, as when the Geiger tube is subjected to radiation from flame, during the half cycle in which terminal 10 is positive, current flows through impedance 12, capacitor 13 and diode 14 to charge capacitor 13 to the polarity indicated. During the succeeding half cycle, when terminal 11 is positive, current flows through Geiger tube 16, winding 17 and parallel capacitor 19, capacitor 13 and impedance 12 to terminal 10. The current flow in this circuit charges capacitor 19 to the polarity indicated. During the next half cycle, when terminal 10 is positive, diode 14 again conducts current and the forward voltage drop across diode 14 is the only voltage applied to the series circuit consisting of output means 15 and Geiger tube 16. Thus the anode to cathode voltage of the Geiger tube is reduced to a low value to quench the Geiger tube, causing the gas medium to become deionized and rendering the Geiger tube again sensitive to an ionizing event on the next half cycle. Thus,

Geiger tube 16 operates in a quenching mode for one half cycle and in a detecting mode for one half cycle of the AC source. During each of the quenching modes, capacitor 19, which is charged in the presence of flame, is effective to maintain relay winding 17 energized. It is only when a flame failure occurs and Geiger tube 16 does not experience an ionizing event during the detecting half cycle that capacitor 19 is discharged to deenergize the winding 17 of the relay.

By virtue of the improved construction of my invention, I am a'ble to achieve relatively high operating voltages, in excess of 200 volts, necessary to operate Geiger tube 16 and yet by virtue of the same components which provide this high operating voltage, I achieve a quenching half cycle for the Geiger tube to insure that the Geiger tube will, once during each full cycle, again be sensitive to the presence of flame.

Since modifications of my invention will be apparent to those skilled in the art, it is intended that the scope of my invention be limited by the scope of the appended claims.

I claim as my invention:

1. In combination with a pair of terminals adapted to be connected to a source of AC voltage,

first circuit means including DC electrical energy storage means and rectification means connected in series to said terminals,

condition detecting means having an anode and a cathode disposed in an ionizable gaseous medium, said detecting means being sensitive to a condition and becoming current conductive upon being subjected thereto,

and second circuit means connecting said detecting,

means in parallel with said rectification means, said detecting means and said rectification means being poled to conduct current on opposite half cycles of the AC source.

2. In combination with a pair of terminals adapted to be connected to a source of AC voltage,

first circuit means including a capacitor and a diode connected in series to said terminals,

condition detecting means having an anode and a cathode disposed in an ionizable gaseous medium, said detecting means being sensitive to a condition and becoming current conductive upon being subjected thereto,

second circuit means connecting said detecting means in parallel with said diode, the anode of said detecting means being connected to the cathode of said diode,

and electrically energizable output means connected to be responsive to a condition established by conduction of said detecting means.

3. The combination as claimed in claim 1 wherein said first circuit means includes current limiting means to limit the peak current flow therein.

4. The combination as claimed in claim 1 including a relay having a winding connected in said second circuit means and having a capacitor connected in parallel with said winding.

5. The combination as claimed in claim 1 wherein said first circuit means includes fuse type current limiting means to limit the peak current flow therein.

6. A flame detector comprising;

a pair of terminals adapted to be connected to a source of AC voltage,

first circuit means including a resistor, a first capacitor,

and a diode connected directly in series to said terminals to charge said first capacitor on a first half cycle of the AC source,

a Geiger tube having an anode and a cathode disposed in an ioniza'ble gaseous medium, said Geiger tube becoming ionized and current conductive from said anode to said cathode upon being subjected to radiation from a flame,

a relay having a winding and switch means,

a second capacitor connected in parallel with said windand second circuit means connecting said relay winding in series circuit with the anode and cathode of said Geiger tube and said series circuit in parallel with said diode, said Geiger tube being connected to conduct current on the other half cycle of the AC source, the voltage of said AC source during said other half cycle and the voltage of said first capacitor serving as a source of operating voltage for said Geiger tube, and said diode serving to short said Geiger tube and said relay Winding during said first half cycle of said AC source to thereby quench said Geiger tube, said relay Winding being maintained energized during said first half cycle of said AC source by virtue of said second capacitor.

No references cited.

ARCHIE R. BORCHELT, Primary Examiner. 

1. IN COMBINATION WITH A PAIR OF TERMINALS ADAPTED TO BE CONNECTED TO A SOURCE OF AC VOLTAGE, FIRST CIRCUIT MEANS INCLUDING DC ELECTRICAL ENERGY STORAGE MEANS AND RECTIFICATION MEANS CONNECTED IN SERIES TO SAID TERMINALS, CONDITION DETECTING MEANS HAVING AN ANODE AND A CATHODE DISPOSED IN AN IONIZABLE GASEOUS MEDIUM, SAID DETECTING MEANS BEING SENSITIVE TO A CONDITION AND BECOMING CURRENT CONDUCTIVE UPON BEING SUBJECTED THERETO, AND SECOND CIRCUIT MEANS CONNECTING SAID DETECTING MEANS IN PARALLEL WITH SAID RECTIFICATION MEANS, SAID DETECTING MEANS AND SAID RECTIFICATION MEANS BEING POLED TO CONDUCT CURRENT ON OPPOSITE HALF CYCLES OF THE AC SOURCE. 